Computers normally includes several types of memories, for example, a cache memory, a main memory, and a secondary storage device (a hard disk drive or the like). Memories capable of performing faster accesses have smaller capacities and are more expensive. In the above-described example, the access speed and the storage capacity increase in order of the cache memory, the main memory, and the secondary storage device. In other words, the cache memory has the highest access speed and the smallest storage capacity and the secondary storage device has the lowest access speed and the largest storage capacity among them. Thus, memories are hierarchized. Specifically, data with a high use frequency is stored in the cache memory, data with a middle use frequency is stored in the main storage device, and data with a low use frequency is stored in the secondary storage device. In this manner, the memory which is to store data thereon is selected depending on the characteristics of the memory, which results in effective use of the memories by the computer.
For example, Jpn. Pat. Appln. KOKAI Publication No. 2008-242944 describes an integrated memory managing apparatus provided in the computer to manage accesses to the cache memory and the main memory in an integrated fashion.
Furthermore, Jpn. Pat. Appln. KOKAI Publication No. 2009-151603 describes a technique of using MRAM as a main storage device and using another nonvolatile memory as a backup.